Let's try this again.
You can get music from a streaming service - such as Amazon HD, Tidal, Spotify, etc) - using a PC, laptop, tablet, or phone. To do this, you download the appropriate app from the streaming service or Google Play or the Apple Store, depending upon what device you are using. The apps are free, and you use them to access the music library of the streaming service you are using.
Most streaming services offer a free trial. Just go to their website and sign up. They will provide instructions for downloading their app.
OK, so now you can stream to that device (assuming it is connected to the internet, either wired or wirelessly). But at this point, you can only play music using that device's analog output. This may be the speaker in the device, or its headphone output...which you can use for headphones or, with the right cable (headphone jack at one end, RCA jacks at the other) you can connect to your stereo...just like any other input (tuner, tape deck, etc). In this scenario, you are using the DAC in the device to convert the digital music sent by the streaming service to an analog signal. Obviously, your device will be tethered to the stereo system in this scenario.
While some devices have decent DACs built into them, generally the sound quality will be better if you use an external DAC. For PCs and mobile devices, you would connect via USB cable from the device to the external DAC, and via RCA interconnect cables from the external DAC to the stereo system. Now the digital music is bypassing the DAC in the device and instead going to the external DAC, where it is converted to analog. As should be obvious, the device is still tethered in this scenario.
The next alternative is to get a stand-alone streamer. This device interfaces to the streaming service in much the same way as using a computer or mobile device. Effectively, it is a special purpose computer for rendering media files. As when using a computer or mobile device, the streamer must be connected to the internet. This can be a hard-wired connection from your router, or via your home wireless network.
However, you need a way to control what you want the streamer to do (simply, to tell it what music you want to hear). The usual approach is to use a computer or mobile device to play this role. The control device will communicate with the streamer via your local network. In this scenario, the control device must be loaded with the streamer's control application (instead of the streaming service's app). Again, easy to do and free. So, for example, if you use a WiiM, the control device(s) would be loaded with the WiiM app. There are other performance benefits with using a dedicated streamer, but a big one is that you are no longer tethered to your system.
Most streamers, including the WiiM (as far as I know) have a built in DAC. So, you can connect the streamer directly to your stereo. Alternatively, you can feed its output to an external DAC, which in turn sends its analog output to your stereo system.